Method of controlling drainage time of beater saturated slurries



United States Patent 3,344,017 METHOD OF CONTROLLING DRAINAGE TIME 0FBEATER SATURATED SLURRIES John M. Lesniak, Millersville, Pa., assignorto Armstrong Cork Company, Lancaster, Pa, a corporation of PennsylvaniaNo Drawing. Filed Mar. 24, 1965, Ser. No. 442,482

7 Claims. (Cl. 162155) This invention re ates generally to improvedcontrol in the processing of fiber slurries which have been beatersaturated with rubber. More particularly, the invention relates to amethod of controlling the drainage time of beater saturated slurrieswhile yielding a sheet product having an improved hand.

In the various methods of beater saturating papermaking fibers, highlevels of rubber normally produce a slowdrainin slurry during the waterremoval step of making sheets or other products from the rubber-coatedpapermaking fibers. Such slow-draining slurries consume undue time insheet formation, require the slowing down of the papermaking wire, andallow the formation of a sheet which is stiff and has a paper-like feel.This is particularly true where the beater saturation process has beencarried out using the alum-ammonia process described in US. Patent No.2,375,245-Pretzel, or using a corresponding alum-caustic process.Although it is known that fasten draining slurries may be produced bypretreating the fibers with decreased quantities of alum, usually as asolution of papermakers alum, this type of control has not been aseificient as desirable in the production of sheets. The use of lowquantities of alum for a given quantity of latex results in undueformation of clumps of rubber on the fibers and in the Water.Accordingly, there is a need for a means of controlling the processingcharacteristics of beater saturated slurries to allow shortprecipitation times, uniform distribution of rubber on the fibers aswell as control of the drainage characteristics of the slurry so thatresulting sheets will be well formed.

It is the primary object of the present invention to supply such amethod. It is another object of the present invention to describe amethod of readily and inexpensively controlling the drainagecharacteristics of beater saturated slurries in order to produce aproduct having particularly good properties.

These objects are accomplished in a surprisingly straightforward andeffective manner. The invention contemplates certain steps to beincorporated into any of the known beater saturating processes involvingforming a slurry of papermaking fibers in water, precipitating a binderon the fibers to form coated fibers, and forming a product from thecoated fibers. The present invention contemplates adding to the slurryof coated fibers a watersoluble salt of a metal in Groups I, II, IV,VII, or VIII of the Periodic Table. The salt will be dissolved in theslurry. There is then added to the salt-treated slurry sufiicient alkalito achieve a pH in the range of 85-115 to form an insoluble hydroxidewith the metal ion from the salt. A product is then formed from theresulting slurry.

The papermaking fibers contemplated by the present invention are knownpapermaking fibers such as asbestos fibers, glass fibers, mineral woolfibers, animal hair, and leather fibers. In addition, the cellulosicfibers may be used such as kraft, rag stocks, soda, semi-chemical,ground-wood, sulfite stock, alpha pulp, cotton linters either hydratedor unhydrated, as well as such fibers as jute, hemp, sisal, strings,chopped canvas, and other such fibers, which may be bleached,semi-bleached, or unbleached.

The fibers will be formed into a papermaking slurry Patented Sept. 26,1967 "ice by known processes of beating and refining, usually in anaqueous medium. The fibers may then be beater saturated by any of theknown methods of accomplishing the deposition of the rubber content of arubber latex onto the surfaces of the papermaking fibers. Such priorprocesses include pretreatment of the papermaking fibers with suchpretreating agents as cationic melamine-formaldehyde resin, polyvinylpyrrolidone, alum, and any other pretreating agents to place thefibersin condition for the deposition thereon of the solids content of arubber latex and provided the pretreating agent is soluble at pH greaterthan 8.5. Preferably there will be used the above-mentioned process ofU.S. 2,375,245Pretzel, or the modification of that process using causticinstead of ammonium hydroxide. The caustic contemplated will bepotassium hydroxide, sodium hydroxide, or mixtures thereof. Thus thefibers preferably will be pretreated with alum, preferably added in theform of a water solution, normally in an amount in the range of 1 to 6parts by weight alum per 1 part by dry weight of the fibers to betreated. The alum solution is added with agitation. Sufiicient causticin the form of a solution of ammonium hydroxide, or more preferablysodium hydroxide or potassium hydroxide will then be added to bring thepH of the fibrous slurry to a range of 6-8, preferably about 7. Therubber latex will then be added to the neutralized slurry, withagitation, whereupon the solids content of the rubber latexprecipitates. The described preferred process of precipitating therubber is particularly apt in the case where unusually large amounts ofrubber are desired.

The binders contemplated by the present invention are those syntheticrubber binder dispersions known to be adaptable in a beater saturationprocess. Typical of these synthetic rubbers are the butadiene-styrenecopolymers (SBR) often containing 30%80% by weight butadiene. Highstyrene butadiene-styrene copolymers may also be used. Thebutadiene-acrylonitrile copolymers, normally containing 50%80% by weightbutadiene and the neoprenes (polychloroprenes) which are polymers of 2-chloro-butadiene-l,3 are also widely used. Homopolymers of butadiene aswell as homopolymers and/ or copolymers of butadiene homologs such asisoprene all can be used to form useful products; the so-called butylrubber latices are useful. Other rubbery and elastomeric substanceswhich can be deposited on fibers may be used in the present method.

Although prior processes sometimes state that they are adaptable to usewith large amounts of rubber, usually 200%650% by weight rubber based onthe dry weight of the fibers, as a practical matter such processes arenot as smooth as they might be. Such large amounts of rubber solids inthe fibrous slurry compared with the amount of fibers produces moreoften than not precipitation of the rubber solids in the water as wellas precipitation of the rubber solids on the fibers. The rubber solidsare thus dispersed in small clots throughout the fibrous slurry. Theresulting slurry may drain either too fast or too slow according to theexact nature of the precipitation of the large amount of rubber. Asmentioned earlier, a fast-draining slurry produces a web which is nothomogeneous. A slow-draining slurry produces a web which is homogeneousbut, due to the fineness of the rubber precipitate, the wire may becomeclogged and the drainage time of the sheet will be too high. If thedrainage time of the sheet is long, that is, if the Canadian 3-gramfreeness is low, both the drainage time and the quality of the resultingsheet may be controlled by the present method. It is a particularadvantage of the present invention that precipitation of rubber in thewater as well as on the fibers does no harm to the processingcharacteristics of the slurry or to the sheet formed therefrom. In fact,with extraordinarily high amounts of rubber, it is a normal and expectedpart of the present method to accept precipitation of the rubber in thewater and to utilize the situation to form a good sheet having animproved hand.

The present invention contemplates adding a watersoluble salt to theslurry of coated papermaking fibers which may or may not have rubberprecipitated in the Water. The water-soluble salts are those whichresult from the reaction of acetic acid or the inorganic mineral acidswith the proper metallic compound. The inorganic mineral acids aretypically hydrochloric acid, nitric acid, and sulfuric acid. Themetallic portionthe cation-01 the water-soluble salt to be added to theslurry will be any of the metals found in the groups of the periodicsystem mentioned earlier. Aluminum and chromium do not work in thecontrol of processing characteristics of the slurry, probably because ofthe ease with which these two metals form anions with oxygen at analkaline pH. The metals which function in the present method appear todo so by virtue of the nature of their behavior after thesalt-eontaining slurry has been made alkaline, to be described below.Typical of the water-soluble salts which operate in the present methodare lead acetate, manganous chloride, ferrous chloride, ferric chloride,calcium chloride, cobalt chloride, nickel chloride, and thecorresponding nitrates and water-soluble sulfates thereof. There shouldalso be mentioned magnesium sulfate, copper sulfate, zinc nitrate,cadmium sulfate, and beryllium sulfate, and the correspondingwater-soluble chlorides thereof.

The water-soluble salts are preferably added in the form of their watersolution, with agitation. The maximum amount of the salt to be added tocontrol the drainage characteristics is determined by the weight of thecation portion of the salt. The weight of the cation portion of the saltshould not exceed about 50% by weight of the uncoated fibers on a drybasis. Larger amounts of the salt are not only wasteful, but may imparta harshness of hand to the finished sheet. As to the minimum amount ofsalt to be added, quite small amounts are effective. Activity of thedifferent operable water-soluble salts will differ, but a reasonableminimum may be established at about 0.1% by weight of the cation portionof the salt based on the Weight of the uncoated fibers.

For ease of distribution of the solution of the Watersoluble salt andwater throughout the slurry containing the precipitated rubber, it ispreferred to use a dilute solution on the order of l%5% by Weight of thesalt in water. This solution will be added with agitation in order todistribute the water-soluble salt thoroughly throughout the slurry.

After the water-soluble salt has been thoroughly distributed throughoutthe slurry of coated fibers, it is necessary to add sufiicient causticto adjust the pH of the slurry to a range 85-115, and preferably to 9.5.Although ammonium hydroxide, sodium hydroxide, or potassium hydroxidemay be used, ammonium hydroxide may form soluble complexes with some ofthe metals used in making the water-soluble metal salt. Potassiumhydroxide is comparatively expensive. For these reasons, sodiumhydroxide is the caustic of choice. Preferably the caustic will be addedin the form of its water solution, the concentration being anyconvenient concentration, a solution of the caustic being a goodaverage. Sufiicient of the caustic solution is added with agitation toestablish a pH within the above-mentioned pH range in the slurry, thetarget pH being 9.5. A pH higher than about 11.5 may unduly harm orreact with the ingredients in the slurry, while a pH below about 8.5 isnot high enough to achieve the full desirable effects of the presentmethod. The pH of the resultant slurry may be checked in known mannerwith a suitable pH meter or test paper. Once the process has becomestabilized in the commercial production of any particular product, theamounts of the ingredients will be known and occasional checks may beall that is required.

The final slurry, with its pH of about 9.5, .is ready for dewatering assoon as the caustic has been thoroughly admixed. A product will beformed from the resulting slurry by removing water therefrom as byintroducing the agitated slurry into a mold, or more preferably, onto apaperrnaking or feltmaking wire or cylinder. The drainagecharacteristics of the particular finished slurry will be found to becontrollable by the amount of water-soluble metal salt that has beenadded within the limits described above. Increased amounts of thewater-soluble salt increase the drainage time and decrease the Canadian3- gram freeness. In accordance with the present method then, it ispossible to decide exactly the drainage characteristics desired of theslurry under preparation, and adjust the water-soluble metal saltaddition accordingly.

The present method lends itself to modifications involving the use ofsynthetic fibers in the form of staple fibers, notoriously difiicult tohandle in beater saturation processes. Synthetic fibers such aspolyamide fibers, polyester fibers, poly(vinyl chloride) fibers, andother hard-tohandle fibers may be added to a slurry immediately afterprecipitation of the rubber as described above. The use of thesesynthetic fibers may be particularly desirable in using theextraordinarily large amounts of rubber contemplated as a modificationof the present method as described and claimed in copending applicationSer. No. 442,481, filed concurrently herewith.

As emphasized above, the method of the present invention particularlyoperates to speed up the drainage time of a slurry which otherwise wouldbe too slow.

The following examples illustrate several embodiments of the invention.All parts are by weight unless otherwise stated.

Example 1 Two parts of refined 6D asbestos was dispersed in 1,850 partsof water. Thirty parts by volume of a 20% aluminum sulfate solution wasthen added with agitation, followed by the addition of sulficient 10%sodium hydroxide solution to obtain a pH in the slurry of 7.0. To theresulting slurry was added a butadiene-styrene copolymer latex (Tylac Ti/I563) in an amount sufiicient to add 6 parts dry weight of rubber. Thisamount is 300% by weight rubber based on the dry weight of the fibers.

After 15 minutes of agitation, all the latex had precipitated onto boththe asbestos and the precipitated aluminum hydroxide.

The resulting slurry was divided into 8 equal portions, each of about250 parts by volume, each containing onequarter part of the originalasbestos fiber. The different portions of the slurry were treated withvarious amounts of a 1.2% solution of magnesium sulfate, followed by theaddition of 3 parts by volume of a 10% sodium hydroxide solution toachieve a pH of 9.5. Table 1 indicates the drainage characteristics ofeach portion of the beater saturated asbestos slurry using differentlevels of magnesium sulfate.

TABLE 1 Canadian stand- Vol. of MgSO solution, ml.: ard freeness Example2 A variety of runs was made using different binders and fibers, thebinder being present in various amounts. Each run was made along thelines of the description in Example 1 in which a 20% solution of alumwas added to the fibrous slurry, the pH brought to 7 with sodiumhydroxide, the latex added with agitation, and sufiicient time allowedfor the solids content of the latex to precipitate on the fibers and inthe water. At this point in the precipitation, all the slurries exceptthat containing 20% by weight of binder based on the weight of thefibers contained precipitated fines which passed right through thedrainage wire and were lost in attempts to make sheets. The addition ofcaustic solution to achieve a pH of 9.5 alone without the prior additionof the water-soluble metallic salt caused the formation of large clumpsfrom which a satisfactory sheet could not be made. However, the additionof a 1% magnesium ion based on the weight of the fibers, followed by thecaustic treatment to a pH of 9.5, produced slurries that were easilyhandleable with no loss of fines and which formed acceptable sheets, allof the slurries then having Canadian standard freenesses in the range of550750.

Table 2 gives the data on the series.

TABLE 2 Percent Volume of Run Binder Type Fiber Binder 20% Alum No.Solution 1 Butadiene-nitn'le Asbestos 300 20 2 Neoprene do 300 15 3Butadiene-nitrile 300 15 terpolymer. 4 Isoprene polymer. 300 13 5 Butylpolymer 300 15 6 Natural rubber. 300 15 7 Butadiene-styrene 500 24copolymer (Tylae TM563). 8 do 200 12.5 9 do d0 r. 300 15 10 do Cottonlinters 300 12.5 11 d0 Cellulose-bleached 20 0.6

sulfide.

0 r do 300 10 16 Butadiene-styrene Unrefined cotton 200 12.7

copolymer llnters. (PBS-2000).

Example 3 Runs were made which duplicated Run 9 in Table 2, save thatdifferent metallic salts were added in different amounts to theprecipitated slurry. The precipitated slurry before treatment wasunsuitable for forming a sheet product due to the large amount ofprecipitated fines which were lost with the white water. The addition ofcaustic alone to a pH of 9.5 caused the formation of large clumps, againunsuitable for sheet formation. However, the addition of a 1% solutionof the metal salt indicated in the amount indicated improved the sheetformation as opposed to either the untreated slurry, or the caustictreated slurry in the absence of the metal salt.

6 Table 3 identifies the metal salt and the volume of 1% by weightsolution used.

TABLE 3 Metal salt: Parts by vol., ml. Lead acetate 2.5 Manganouschloride 5 Ferrous chloride 5 Ferric chloride 10 Calcium chloride 25Cobaltous chloride 5 Nickelous chloride 2.5 Magnesium sulfate 1.5 Coppersulfate 5 Zinc nitrate 2 Cadmium sulfate 2.5 Beryllium sulfate 2.5Barium chloride 20 The large amount of calcium chloride and bariumchloride is apparently needed due to the presence of sulfate ion in theslurry.

I claim:

1. In the method of making beater saturated products by forming a slurryof fibes in water, precipitating a rubber binder on said fibers to formcoated fibers, and forming a product from the coated fibers, theimproved method of controlling the drainage time of the slurry of coatedfibers which comprises adding to said slurry of coated fibers awater-soluble salt selected from the group consisting of metals inGroups I, II, IV, VII, and VIII of the Periodic Table, adding suflicientalkali to the salttreated slurry to achieve a pH in the range of -115 toform an insoluble hydroxide with the metal ion from the salt, andforming a product from the resulting slurry.

2. A method according to claim 1 in which said rubber binder comprises abutadiene-styrene copolymer.

3. A method according to claim 1 in which said alkali comprises sodiumhydroxide.

4. A method according to claim 1 in which said watersoluble saltcomprises magnesium sulfate.

5. A method according to claim 1 in which said pH is 9.5.

6. A method according to claim 1 in which said fibers comprise asbestosfibers.

7. The product formed by the method of claim 1.

References Cited UNITED STATES PATENTS 2,375,245 5/1945 Pretzel 162-169S. LEON BASHORE, Primary Examiner.

1. IN THE METHOD OF MAKING BEATER SATURATED PRODUCTS BY FORMING A SLURRYOF FIBES IN WATER, PRECIPITATING A RUBBER BINDER ON SAID FIBERS TO FORMCOATED FIBERS, AND FORMING A PRODUCT FROM THE COATED FIBERS, THEIMPROVED METHOD OF CONTROLLING TH DRAINAGE TIME OF THE SLURRY OF COATEDFIBERS WHICH COMPRISES ADDING TO SAID SLURRY OF COATED FIBERS AWATER-SOLUBLE SALT SELECTED FROM THE GROUP CONSISTING OF METALS INGROUSP I, II, IV, VII, AND VIII OF THE PERIODIC TABLE, ADDING SUFFICIENTALKALI TO THE SALTTREATED SLURRY TO ACHIEVE A PH IN THE RANGE OF8.5-11.5 TO FORM AN INSOLUBLE HYDROXIDE WITH THE METAL ION FROM THESALT, AND FORMING A PRODUCT FROM THE RESULTING SLURRY.